Process for producing microfibrillated cellulose

Abstract

A process for treating cellulosic fibers comprises mechanically pre-treating the fibers followed by treating the fibers with an enzyme and thereafter mixing the fibers with a solution comprising an alkali metal hydroxide followed by mechanically treating the fibers to form microfibrillated cellulose. In this way it is possible to produce microfibrillated cellulose (MFC) in an improved and energy efficient way.

The invention claimed is: 
     
       1. A process for treating cellulosic fibres comprising:
 mechanically pre-treating the fibres, 
 treating the mechanically pre-treated fibres with an enzyme, 
 mixing the enzymatically treated fibres with a solution comprising an alkali metal hydroxide and a zinc salt in order to make the fibres expand and 
 adding a chemical selected from surface active agents, bentonite, TiO 2 , or CMC to prevent shrinkage of the expanded fibres; 
 decreasing a concentration of the alkali metal hydroxide to regenerate dissolved fibrils or particles by adding water, or an acid after adding the chemical; 
 mechanically treating the expanded fibres to form microfibrillated cellulose. 
 
     
     
       2. A process for treating cellulosic fibres comprising:
 mechanically pre-treating the fibres; 
 treating the mechanically pre-treated fibres with an enzyme; 
 mixing the enzymatically treated fibres with a solution comprising an alkali metal hydroxide and a zinc salt in order to make the fibres expand; 
 mechanically treating the expanded fibres to prevent shrinkage; 
 decreasing a concentration of the alkali metal hydroxide to regenerate dissolved fibrils or particles by adding water, or an acid after mechanically treating the expanded fibres; and 
 mechanically treating the expanded fibres to form microfibrillated cellulose after decreasing the concentration of the alkali metal hydroxide. 
 
     
     
       3. The process according to  claim 2  wherein the concentration of the alkali metal hydroxide is between 4-18% by total weight. 
     
     
       4. The process according to  claim 2  wherein the concentration of zinc salt is between 0.1-2% by weight. 
     
     
       5. The process according to  claim 2  wherein the fibres are mechanically pre-treated by shredding or refining. 
     
     
       6. The process according to  claim 5  wherein the fibres are treated at a consistency of between 2.5-40% by total weight during the shredding or refining. 
     
     
       7. The process according to  claim 2  wherein the temperature during the treatment with the solution is between 0-15° C. 
     
     
       8. The process according to  claim 2  wherein the alkali metal hydroxide is sodium hydroxide. 
     
     
       9. The process according to  claim 2  wherein the zinc salt is zinc oxide. 
     
     
       10. The process according to  claim 2  wherein the enzyme is cellulase. 
     
     
       11. The process according to  claim 2  wherein an enzyme affecting hemicellulose or an enzyme affecting cellulose is added before or during the mechanical pre-treatment of the fibres. 
     
     
       12. The process according to  claim 2  wherein the fibres are fibres of kraft pulp. 
     
     
       13. The process according to  claim 2  wherein the concentration of the alkali metal hydroxide is between 5-9% by total weight. 
     
     
       14. The process according to  claim 2  wherein the concentration of zinc salt is between 0.5-1.3% by weight. 
     
     
       15. The process according to  claim 11  wherein the enzyme affecting hemicelluloses is xylanase. 
     
     
       16. The process according to  claim 11  wherein the enzyme affecting cellulose is cellulase. 
     
     
       17. The process according to  claim 2  wherein a total energy consumption is less than a total energy consumption of a process without mixing the enzymatically treated fibres with the solution comprising the alkali metal hydroxide and the zinc salt. 
     
     
       18. The process according to  claim 2  further comprising adding a chemical selected from the group consisting of surface active agents, bentonite, TiO 2 , or CMC to prevent shrinkage of the expanded fibres.